The invention relates to an improved method for the manufacture of particleboard from a cellulose-containing material using an aminoplast or an amino resin adhesive as the bonding agent, as well as a novel bonding agent suitable for use in such a method. As used herein, the term `particleboard` shall be understood to mean a composition board made up of individual, wood particles such as chips, flakes, fibers, and the like, or of any other particulate cellulose-based material which have been coated with a resin bonding agent and formed into shape by pressure and heat.
It is known to manufacture particleboard with an urea-formaldehyde resin as the bonding agent, wherein the molar ratio of formaldehyde to urea is typically in the range of about 1.5:1 to 1.9:1. However, if this formaldehyde to urea molar ratio is above 1.3, the resulting particleboard may continue to release formaldehyde into the environment after manufacture, and even after it is applied in its ultimate use, creating the potential for health or environmental problems. Particleboard manufactured in accordance with the known methods typically has a formaldehyde emission in the range of between about 0.03 and 0.06 (FESYP perforator test, wt % of formaldehyde released).
Applicant has found that it is possible to produce particleboard having a very low formaldehyde emission level by using a urea-formaldehyde resin having a molar ratio of formaldehyde to urea of about 1.1:1, but the mechanical properties of particleboard by such method are unsatisfactory, particularly if the boards are stacked after pressing while they are still warm. An important disadvantage is also that, regardless of stacking, the boards show a large degree of swelling when in contact with water. Although these unsatisfactory mechanical properties can be improved by using more than the conventional amount of bonding agent, this overcomes the disadvantage only to a limited extent.